System for counteracting undesired oscillations in alternating current circuits



Nov. 10, 1931, T. H. BURNS 1,831,340

SYSTEM FOR COUNTERACTING UNDESIRED OSCILLATIONS IN ALTERNATING CURRENTCIRCUITS Filed April 28, 1926 illlll ll INVENTOR ThOmasHBurns ATTORNEYPatented Nov. 10, 1931 UNITED STATES PATENT, OFFICE 1 THOMAS H. Bonus,on NEWARK, ew JERSEY,

svsrmr ro'R COUNTERACTIN'G unnnsmnn OSCIILLATIONS IN 'ALTERNATINGCURRENTi CIRCUITS a,

' Application filed Apri1 28, 1926. Serial No. 105,059.

The invention relates to a system for the prevention of undesired orstray oscillations or oscillations of regeneration in an alternatingcurrent circuit, and more particularly to the counteracting inelectrical circuits, as

radio frequency receiving and transmitting circuits, of objectionableoscillations set up therein. In tuned'radio' frequency receivingcircuits, for example, such as the typicalcircuitsembodying one or morestages of radio frequency amplification, it frequently occurs in theoperation of the same that disturbing oscillations develop coupling witha circuit one or more-stabilizf 'ing circuits, each consisting of twocircuit portions wherein are set up Voltages counters acting'inducedvoltages of regeneration developed in the part of. said originaloscillating circuit with which each respective circuit portion iscoupled. Heretofore, it has been proposed to providein the originalcircuit an exactly opposed impedance, or to provide therein a definiteopposing electromotive force. Both of these expedients, if theadjustments are only slightly out, can be offset by raising or bylowering the total admittance of the tuned'grid circuit-and so permit oftuning at two different dialsettings; The result is broad tuning andinability completely to eliminateincipient lations unless a considerableexcess of negaas a result of the produc- I 'tion of a regenerated wave.These oscillaundesired osci'l-- tive impedance and consequent low.efficiency are allowed. The novel system on the contrary relies on noexact impedance effect with current variable, nor fixed impedance withits current controlled by some other part of, the circuit, due tomagnetic couplingor direct series connection, but fixed impedance andcontrolled by magnetic utilizes an arbitrary coupling due toneutralizationof the magnetic coupling nor by direct connection to someo'therpart of the circuit, but b coil system.

The nature of the invention, however, will best be understood whendescribed in connection with the accompanying drawing which is adiagrammatic representation of atypical radio receiving circuit.embodying, for example, two stages of radio frequency amplification andadetector, with the novel stabilizing circuit associated with gridinductances thereof;

Referrin illustrated g to the drawing, the invention is as applied to atuned radio frequency circuit embodying by way of example two stages ofradio frequency amplification;

and to this end comprises generally the first transformer 10, amplifyingtubes 11 and a detector tube 12, with intermediate amplifyingtransformers densers 14, The'particula'r circuit set forth 13 and thetuning conis shown merely by way of example; and it is to beunderstood't-hat theinvention is not restrlcted to the particularcharacter of circuit shown but is applicableto various circuits whereindisturbing osclllatlons may deside source. 7

To overcomethe effect ofsuch undesired :velop due to certain conditionsor characterlstics inherent 111 the circu-it'or from anoutoscillationsthere is arranged to be associated with said circuit thehereindes'cribed stabilizing circuit, which maybe applied in multiplewhen addition This alstages of amplification are stabilizing circuitcomprises i variable current, not w y a voltage balance in a tapped aninductance 20 and an inductance 21, across which latter is bridged avariable condenser 22the inductance 20 being connected to saidinductance 21 substantially at the midpoint of the same in order thatthe values of the inductance in the portion thus divided may besubstantially equal. A condenser 23, preferably variable, is included inseries with the inductance 20 and a junction point 25. Two closedcircuit portions are thereby formed of the stabilizing circuit, the onecomprising the inductance 21, condenser 22 and leads to connect the sameto the junction point 25 thru which it is connected by a lead 26 to theradio frequency circuit. The other closed portion comprises theinductance 20, the condenser 23 and the two parallel paths thruinductance half 24, and inductan e half 27 and condenser 22 to thejunction point 25 as well as leads to effect the connections. have foundfor a tuned radio frequency amlified circuit, having a range of from 200to 500 meters with transformers of 6 to 60 turns on 3" diameter core.that the inductance 21 should consist'of a coil of 2" diameter and ofapproximately 35 turns. while the inductance 20 might consistsubstantially of a coil of 3" diameter and of 4 turns, with capacitiesof the condensers 22 and 23 varying approximately from 0 to .0005 mfd.

The aforesaid inductanccs 20 and 21, which may be variable if desired,are to be coupled in electro-magnetic relationship with any inductancesof the radio frequency circuit between which a tendency towardregeneration exists, for example in this case. the inductance 20 may becoupled and preferably in close relationship with the secondary of thefirst transformer 10 while the inductance 21 is to be coupled but moreloosely with the secondary of 'the'first of the amplifying'transformers13. The stabilizing circuit as a whole is connected thru the junctionpoint 25 and lead 26 to the receiving circuit at a point ofpredetermined potential; or the jun ction-point may be directlygrounded. It is to be understood that the relationship of theinductances 20 and 21 respectively to the secondary of the firsttransformer'10 and secondary of transformer 13 is such that the magneticeffects due to induced voltages of regeneration set up in one ofacoupled pair are counteracted by the opposingefiects introduced intothe other pair, which in turn transmits the counteraction to theoriginal oscillating circuit.

As set forth, the stabilizing circuit consists of two portions eachadapted to counterbalance an induced voltage such as may be caused byregeneration in'their respective coupled circuits. Instantaneous currentflowing from inductance 20 to the junction point 25 divides equally attap 28, due to the equal impedances of the paths having leading andlagging reactances to currents,

particular condition of circuit balance.-

said paths comprising top point 28,. inductance 27 condenser 22 andjunction point 25, and tap point 28, inductance 24 and the junctionpoint 25 respectively; as adjusted by condenser 22 and indicated or bythe resultant tone. The inductances 2a and27, as stated, are equal andtherefore the magnetic effects of the equal currents are equal andopposite or neutralized. This neutralizes the magnetic coupling betweenthe two circuit portions. The currents prevailing in each portion arevari ble and independent, due to neutralization of magnetic couplingbetween them; and each current assumes its proper value as may be shownby the following considerations of the actions involved. An inducedvoltage of regeneration predominating in inductance 20 will increase thecurrent in the correspond- 1 ing circuit portion and therefore thevoltage across'the impedance of inductance 24. The increased voltage dueto potential balancing in the'other circuit portion will send back avoltage counteracting the initial induced voltage. This new current willalter slight- V ly the neutralized magnetic coupling and may be adjustedby condenser 22 so that impedance of inductance 24 will be equal to theresultant impedance of inductance portion 27 and capacityof condenser23. Similarly,

an induced voltage predominating in inductance 21 will increase thecurrent in its corresponding circuit portion. The decrease of currentsfollow by like reasoning.

by proper balance The approximate proportion of currents is obtained 1';

by means of condenser 23 which thereafter may remain practically fixed.Thus, both currents reach their proper vvalue for any The currentprevailing in either inductance-20 or 21' automatically adjusts itselfto counter balance the induced regenerated current in the circuitcoupled therewith, without relation to the other current or any otherpart of the general circuit. This results in a highly efi ficientcircuit, perfectly balanced.

While the embodiment of the invention is herein shown as appliedspecifically to a radio frequency circuit, it is to be understood thatthe same is equally applicableto the counteracting of undesired orstrayoscillationsof regeneration in audio frequency circuits.

'I claim s 1. In a system for counteracting undesired oscillations in aradio frequency circuit of two stages of tuned radio frequencyamplification: a stabilizing circuit including two closed circuitportions each containing an inductance electromagnetic'ally coupledrespectively to two of the grid circuits of the radio frequency circuitand also thru a junction point; variable condensers included in both ofthe circuit portions; and leads connecting the two portions to'eachother in manner such that the inductance of the one is connectedsubstantially at the midpoint of the inductance of the other.

2. In a system for counteracting undesired oscillations in a radiofrequency circuit in- I eluding a tuning portion: a stabilizing cir-THOMAS H. BURNS.

